Coating apparatus

ABSTRACT

Apparatus for applying liquid material to the edges of a die of semiconductor material mounted between two conductive plugs. The plugs and intervening die constitute a semiconductor element which is fed from a vibratory feeder to a transfer wheel and then gripped between a pair of opposed spindles of a conveyor wheel. The conveyor wheel carries the semiconductor element with the spindles rotating into a work station. At the work station the edges of the rotating semiconductor die come into contact with continuously moving filamentary material which passes through a vessel containing liquid coating material before contacting the semiconductor element at the work station. The filamentary material picks up liquid material from the vessel and transfers it to the edges of the die of the semiconductor element at the work station.

United States Patent [191 Van Der Schoot [s41 COATING APPARATUS [75] Inventor: Theodore H. Van Der Schoot, Deering, NH.

[73] Assigneez' GTE Sylvania Incorporated, New

York,N.Y.

22 Filed:. Feb.23, 1971 21 App1.N0.:117,959

[52] U.S. Cl. ..1l8/230, 118/232, 118/263 [51] Int. Cl ..B05c 1/02 [58] Field of Search ..118/230, 232, 244, 118/258, 263, 420, 319

[56] References Cited 9 UNITED STATES PATENTS 2,289,263 7/1942 Hart ..l18/230 768,873 8/1904 Bell ..1 18/230 X 2,623,494 12/1952 Scherer ..1 18/230 X 3,251,339 5/1966 Whitfield. ..118/420 X 7 791,745 6/1905 Bailey; ..l18/23O 1,448,726 3/1923 Cheney ..118/258 X Quillfeldt ..1 18/230 X May 29, 1973 2,329,263 9/1943 Gladfelter et al ..1l8/23O Primary Examiner-Mervin Stein Attorney-Norman J. OMalley, Elmer J. Nealon and David M. Keay 5 7 ABSTRACT Apparatus for applying liquid material to the edges of a die of semiconductor material mounted between two conductive plugs. The plugs and intervening die constitute a semiconductor element which is fed from a vibratory feeder to a transfer wheel and then gripped between a pair of opposed spindles of a conveyor wheel. The conveyor wheel carries the semiconductor element with the spindles rotating into a work station. At the work station the edges of the rotating semiconductor die come into contact with continuously moving filamentary material which passes through a vessel containing liquid coating material before contacting the semiconductor element at the work station. The filamentary material picks up liquid material from the vessel and transfers it to the edges of the die of the semiconductor element at the work station.

18 Claims, 14 Drawing Figures PATENTEB W 2 9 I973 SHEET 1 BF 7 v INVI'IN'I'OR THEODORE H. VAN DER SCHOOT BY W 7 7 7 AGENT PATENTEL IJLYZQISYS SHEET 2 [IF 7 Fig. 2.

w H w N m H. E m m m AGENT IPATENTEWZQ'QH 3.735.732

SHEET 3 UP 7 SUPPLY 105 CONTROL MOTOR INVENTOR THEODORE H. VAN DER SCHOOT AGENT PATENTELERYZQISH 3 735,732

SHEET 6 0F 7 INVEN'I'OR THEODORE H VAN DER SCHOOT AGENT PATENI m 2 91975 E INVENTOR THEODORE H. VAN DER SCHOOT AGENT PATENTEW-YQQ'QYEF 3,735,732

SHEETSUF? INVENTOR THEODORE H. VAN DER SCHOOT EM 747 A4 AGENT 1 COATING APPARATUS BACKGROUND OF THE INVENTION This invention relates to apparatus for applying liquid to portions of articles. More particularly, it is concerned with apparatus for applying protective material in liquid form to a predetermined region of a semiconductor element.

In the manufacture of various types of semiconductor diodes or rectifiers a wafer of semiconductor material is treated by the diffusion of conductivity type imparting materials into one or both major surfaces to form a rectifying P-N junction. Then the wafer is divided into individual chips or dice. Each die is mounted between conductive plugs to provide a semiconductor element in which one of the plugs serves as an anode contact and the other as a cathode contact. Depending upon the electrical characteristics of a semiconductor element and its intended use, an element may be mounted in any of various enclosures either as a single element or in combination with several elements or other components.

Since the individual semiconductor dice are obtained by dividing a wafer having a continuous P-N junction, the edge surfaces of each die contain the exposed edges of its P-N junction. In order to prevent degradation of the electrical characteristics of the semiconductor elements the edge surfaces of each die are protected by a protective coating. Protective material is applied to the edge surfaces of the dice in liquid form, and then the semiconductor elements are baked to cure and harden the protective material.

It has been the practice to apply the protective liquid material manually to the edge surfaces of the dice in the region of the semiconductor elements between the cathode and the anode plugs. The coated semiconductor elements are then carefully placed in a boat or tray and heat treated in an oven to harden the protective material. Because of the small size of the semiconductor elements (typically having a maximum dimension of the order of one-tenth of an inch) it has been a difficult and time-consuming operation to apply the liquid to the exposed edges of the dice and place the semiconductor elements in boats without causing some liquid to flow onto the anode and cathode plugs so as to interfere with the subsequent electrical connections to the elements.

SUMMARY OF THE INVENTION Consistent application of accurately controlled quantities of liquid material to precisely predetermined regions of articles such as semiconductor elements is provided by automatic coating apparatus in accordance with the present invention. The apparatus includes a carrying means for presenting an article to be coated at a work station and rotating means for rotating the article while the article is located at the work station. A supply of the liquid material to be applied is contained in a vessel. In one embodiment of the invention, filamentary material is fed from a supply of filamentary material by an appropriate feeding means so as to pass the filamentary material through the liquid material in the vessel and into contact with the article located at the work station. The filamentary material picks up liqv uid material from the vessel and carries the liquid material into contact with the rotating article at the work station thereby transferring liquid material to the region of the article which comes into contact with the filamentary material. The amount of liquid material transferred to the article is regulated by appropriate adjustment of the time the article remains at the work station and the linear speed of the filamentary material.

In an alternative embodiment of the invention a circular plate having a plurality of flexible members arranged along its periphery is employed in place of fila mentary material to transfer liquid material from the vessel to the article located at the work station. The circular plate is supported in a support means to enable rotation about its axis with flexible members on the lowermost portion of the circular plate in the liquid material and with flexible members on another portion of the circular plate in contact with the article located at the work station. The circular plate is rotated by suitable means whereby the flexible members pick up liquid material from the vessel and carry it into contact with the rotating article at the work station.

In one form of apparatus for conveying articles they are fed from a supply of articles to a transfer wheel which carries the articles in succession through a loading station where they are gripped between holding members of a conveyor wheel. The conveyor wheel carries the articles in succession to the work station at which the liquid material is applied, and then to an un' loading station. At the unloading station the holding members release the articles which drop into receptacles in trays being passed beneath the unloading station.

BRIEF DESCRIPTION OF THE DRAWINGS Additional objects, features, and advantages of coating apparatus in accordance with the present invention will be apparent from the following detailed discussion together with the accompanying drawings wherein:

FIG. 1 is a perspective view illustrating coating apparatus in accordance with the invention with portions removed to expose the principal significant mechanisms;

FIG. 2 is a plan view of the coating apparatus of FIG.

FIG. 3 is a perspective view of a semiconductor element of the type to which liquid material is applied by the apparatus illustrated;-

FIG. 4 is a plan view of a portion of the apparatus illustrating details of the transfer and conveyor wheels in the vicinity of the loading station;

FIG. 5 is a front elevational view of a portion of the apparatus with some elements broken away to show details of the transfer and conveyor wheels;

FIG. 6 is a front elevational view of a portion of the apparatus illustrating elements of the mechanisms for controlling the holding members of the conveyor wheel;

FIG. 7 is a perspective view illustrating certain details of the conveyor wheel;

FIG. 8 is a view partially in cross-section illustrating the manner in which a pair of holding members of the conveyor wheel grip a semiconductor element to be coated;

FIG. 9 is a side elevational view partially in crosssection illustrating portions of the conveyor wheel and the mechanism for releasing a semiconductor element from the holding members at the unloading station;

FIG. 10 is a'front elevational view with portions broken away to show details of the work station at which the filamentary material, after passing through a vessel containing liquid material, transfers the liquid material to a semiconductor element held by holding members of the conveyor wheel;

FIG..1 1 is a perspective view illustrating the portions of the apparatus for feeding and controlling the movement of trays having receptacles for receiving the coated semiconductor elements released from the holding members at the unloading station;

FIG. 12 is a view partially in cross-section illustrating the trays for receiving semiconductor elements;

FIG. 13 is a schematic diagram of the mechanism for controlling the movement of trays passing beneath the unloading station; and

FIG. 14 is a front elevational view similar to that of FIG. illustrating a modification of the coating apparatus of the invention.

DETAILED DESCRIPTION OF THE INVENTION General Description A coating apparatus in accordance with the present invention is illustrated in the perspective view of FIG. 1 and the plan view of FIG. 2. One of the semiconductor elements 10 which is to have a coating of liquid material applied to its central region by the apparatus is shown in FIG. 3.

A quantity of semiconductor elements 10, as shown in FIG. 3, are placed in a vibratory bowl feeder 11 which presents them one at a time in end-to-end relationship to a transfer wheel 12. The transfer wheel 12 indexes periodically, and during each dwell period between indexes a semiconductor element is placed in a slot 13 (FIG. 1) in the periphery of the transfer wheel. The transfer wheel 12 carries the semiconductor elements to a loading station 14 (FIG. 1). A conveyor wheel 15 which indexes in synchronism with the transfer wheel moves holding membersl6 and 17 which are mounted therein into the loading station. During each dwell period a semiconductor element is transferred from the slot in the transfer wheel 12 which is located at the loading station 14 to the pair of holding members 16 and 17 of the conveyor wheel 15 which is located at the loading station.

During succeeding indexes the conveyor wheel 15 moves the semiconductor element 10 out of the loading station and into a work station 20. During the course of this movement and while the semiconductor element is at the work station, the holding members 16 and 17 are rotated. At the work station, the central region of the rotating semiconductor element comes into contact with filamentary material 21 which is passing continuously through a vessel 22 (FIG. 1) containing liquid coating material. Liquid material transfers from the filamentary material 21 to the central region of the semiconductor element 10.

The coated semiconductor element 10 is carried from the work station during subsequent indexes of the conveyor wheel and moved to an unloading station 23 (FIG. 1) at which point it is released from between the holding members 16 and 17. The semiconductor element drops into a cavity in a tray 24 which is located beneath the unloading station. The trays are fed end-toend along a track 25 which passes beneath the unloading station.

A supply of trays is positioned on a chute 26, and trays slide in sequence from the chute to the track 25. The trays are indexed along the track 25 so that a cavity is located beneath the unloading station 23 to receive each semiconductor element when it is released. The loaded trays are diverted from the track onto an exit chute 27. The trays are removed from the exit chute 27 and placed in a suitable oven in order to cure the liquid material and thus provide a permanent protective coating around the central region of each semiconductor element.

The apparatus is operated by a motor and drive mechanism 28. The conveyor wheel 15 is centrally mounted on an indexing shaft 29 from the drive mechanism 28 which indexes periodically to rotate the shaft through an increment of a circle. The transfer wheel 12 is mounted on a shaft 30 which is coupled directly to the indexing shaft 29 by gears 31 and 32 and belt 33 and thus rotates in synchronism with the conveyor wheel. A continuously rotating shaft 34 from the drive mechanism 28 rotates a cam shaft 35 one revolution for each complete index and dwell cycle of the indexing shaft 29.

Semiconductor Element A semiconductor element 10 to which liquid material is to be applied is illustrated in detail in FIG. 3. The semiconductor element includes a chip or die 40 of semiconductor material, for example, germanium or silicon, having a'rectifying P-N junction thereacross parallel to its major surfaces. The edges of the junction are exposed at the periphery of the chip. The semiconductor chip is mounted between two conductive plugs 41 and 42 which make ohmic connection to the chip at opposite sides of the P-N junction.

Since the exposed edges of the junction are vulnerable to shorting, contamination, and other deleterious conditions, it is important that the junction be protected before the semiconductor element is further processed by mounting in an enclosure either singly or in combination with other semiconductor elements or other electrical components. The apparatus of the invention applies a small quantity of protective material in liquid form about the periphery of the die 40. The

rangement including the vibratory feeder 11, the transv fer wheel 12, and the conveyor wheel 15. Semiconductor elements move up the ramp 45 (FIG. 2) of the vibratory feeder 11 by virtue of the action of the vibratory bowl. The configuration of the ramp causes the semiconductor elements to become aligned in end-toend relationship. The semiconductor elements pass from the ramp 45 of the vibratory feeder onto a horizontal track 46 (FIG. 2) which, as shown more clearly in FIG. 4, continues through a horiztonal tube 47 to a pickup point at which the semiconductor elements are received by the transfer wheel 12. The semiconductor elements are urged along the tube by the continuous passage of air or nitrogen introduced under slight pressure by means not shown.

The transfer wheel 12, as best seen in FIGS. 4, 5, and 6 in addition to FIG, 1, is a flat, circular, vertically disposed plate having a plurality of slots 13 spaced about its periphery. The transfer wheel 12 is rotated during an index period through an increment equal to the spacing between two adjacent slots and remains stationary during its dwell period. The shaft 30 on which the transfer wheel 12 is mountedis rotated by the indexing shaft 29 through the gears 31 and 32 and belt 33.

During a dwell period, a slot 13 at the edge of the transfer wheel'16 is located at the pickup station adjacent the end of the horizontal track 46 from the vibratory feeder 11. A semiconductor element, urged by the vibratory action of the feeder 11, and by the flow of air along the tube 47, moves into the slot 13 and is stopped by a guide plate 50. When the transfer wheel 12 indexes, the semiconductor element carried in the slot 13 is prevented from moving sideways by the guide plates 50 and 51.

The transfer wheel indexes during subsequent cycles until the semiconductor element is carried into the loading station 14 for transfer to the conveyor wheel 15. Various details of the conveyor wheel are shown in FIGS. 1, 4, 5, 6, and 7. The conveyor wheel 15 includes two circular plates 52 and 53 which are integral with a hub 54 affixed to the shaft 29 which passes through the horizontal axis of the wheel. The first plate 52 carries a plurality of spindles 16 which are equally spaced in a circular-pattern adjacent the periphery of the plate. The spindles 16 are mounted in the plate 52 in bearings so as to permit rotation about their horizontally disposed axes. A pulley 55 is fixed to each spindle -16 at its outer end.

Equally spaced adjacent the periphery of the second plate 53 are a like plurality of spindles 17 each of which is positioned opposite one of the spindles of the first set. These spindles 17 are each mounted in bearings to permit rotation about their axis, and the bearings are mounted in a sleeve 56 to permit linear movement of the spindles with respect to the plate 53 along the direction of their axes. Each spindle 17 of the second set is urged toward the spindle 16 of the first set with which it is paired by a compression spring 57.

A retaining ring 58 at the outer end of each spindle 17 of the second set is engaged by one end of a lever arm 60 which is pivotally mounted on a block 61 fixed to the second plate 53. The lever arm 60 lies along a diameter of the circular second plate 53 and a roller 62 is mounted adjacent its inner end. The position of a second spindle 17 along its axis with respect to each associated first spindle 16 is controlled by the tips of pickup and release lever arms 63 and 64 and a roller guide 65 as they bear against the rollers 62.

The action of the pickup and release lever arms 63 and 64 in controlling the axial movement of the spindles 17 of the second set can best be understood from the showings of the release lever arm 64 as illustrated in- FIGS. 1, 7, and 9. The release lever arm 64 is arranged so as to impart linear movement to the spindle located at the unloading station 23. The release lever arm 64 is pivotally mounted on a rod 66. A cam follower 67 at one end of the lever arm is held against a relase cam 68 fixed to the continuously rotating cam shaft 35 by a tension spring 69. The upper end of the lever arm has a tip 70 for bearing against the roller 62 at the inner end of a spindle lever arm 60. As can be seen in FIG. 9 the rise and fall of the cam follower 67 as determined by the release cam 68 causes the spindle 17 to move axially.

A similar arrangement of the pickup lever arm 63 as shown in FIG. 1 operates through a pickup cam 71 fixed to the cam shaft 35 to impart linear movement to the spindle 17 located at the loading station 14.

The two spindles 16 and 17, or holding members, of each pair of spindles are shown gripping a semiconductor element 10 in FIG. 8. The end surfaces of the spindles are countersunk or concave, and are slightly larger in diameter than the plugs 41 and 42. The amount of linear movement of the second spindle 17 toward the fixed first spindle 16 is such as to provide spacing between the spindle ends which is slightly less than the length of a semiconductor element. Thus, a semiconductor element 10 may be held between the pair of spindles.

The conveyor wheel 15 and its associated mechanisms operate in the following manner to cause a pair of spindles to pick up a semiconductor element from the transfer wheel 12 at the loading station 14, carry the semiconductor element through the work station 20, and release the semiconductor element at the unloading station 23. As a pair of spindles 16 and 17 are moved from the unloading station 23 to the loading station 14, the surface of the roller guide 65 bears against the roller 62 retracting the second spindle 17. The second spindle is retracted sufficiently to insure that the spindle will not interfere with the transfer wheel 12 and that when it reaches the loading station it will be spaced from the end face of the first spindle l6 sufficiently to accommodate a semiconductor element 10 between them.

As the spindle 17 moves into the loading station, the tip of the pickup lever arm 63, as positioned by the pickup cam 71, contacts the roller 62 so as to retract the spindle 17. During the dwell period while the spindles 16 and 17 are at the loading station, the pickup cam 63 permits the spring 57 to urge the second spindle 17 toward the opposite spindle 16 so that the semiconductor element in the slot of the transfer wheel is gripped by the spindles. On the subsequent index of the transfer wheel 12 and conveyor wheel 15, the semiconductor element 10 is carried from the slot of the transfer wheel held between the opposed spindles.

As the conveyor wheel indexes, the semiconductor element 10 is carried with the rotating conveyor wheel 15. At a point in its movement, the pulley 55 of the first spindle 16 of the pair comes in contact with a belt 75 which is continuously driven by a motor 76 as variously seen in FIGS. 1, 2, 4, 5, 6, and 7. This arrangement causes the first spindle 16 to rotate in the direction indicated in FIG. 10. Rotation of the spindle continues as the conveyor wheel 15 rotates as long as the pulley 55 bears against the belt 75. Rotation of the first spindle 16 causes the semiconductor element and the other spindle 17 to rotate. By virtue of the concave faces of the spindles, the cylinderically shaped semiconductor element tends to become aligned with its axis along the axis of the spindle, in the event that it is not quite so aligned when picked up at the loading station.

The spindles 16 and 17 gripping the semiconductor element between them continue their movement with the conveyor wheel 15. During one dwell period the spindles and semiconductor'element are located at the work station 20 at which the liquid material is applied as will be explained hereinbelow. During the dwell period when the semiconductor element is at the unloading station 23, the release cam 68 causes the second spindle 17 to be retracted and the semiconductor element drops from between the spindles 16 and 17. As the spindles 16 and 17 leave the unloading station 23, the roller 62 bears against the surface of the roller guide 65 as explained previously.

As shown in the figures the transfer wheel has 64 semiconductor element receiving slots 13 and the conveyor wheel has 16 pairs of spindles l6 and 17. That is, during each index period the conveyor wheel is rotated 22.5 and the transfer wheel is rotated 5.625.

Liquid Applying Mechanism The mechanism for applying the liquid material to a semiconductor element while it is located at the work station is shown in FIGS. 1, 5, 6, 7, and 10. The semiconductor element is at the work station 20 during the dwell period when it is at the same horizontal level as the central axis of the conveyor wheel 15. At this point the filamentary material 21 comes into contact with the semiconductor element.

The filamentary material 21 passes from a supply reel 80, over a capstan 81, through the vessel 22 containing the liquid material 83, around a pulley 84, and onto a take-up reel 85. The capstan is driven by a variablespeed electrical motor 82 and the take-up reel is driven by a torque motor 86, both of which are shown in FIG. 2.

The liquid material is contained in a chamber of the vessel 22. Thechamber is supplied by a reservoir 87 in order to maintain the liquid in the chamber at a predetermined fixed level. As shown most clearly in FIG. 10, the filamentary material is guided through the chamber by a passageway 88 in the vessel and by a guide 89. Filamentary material passes directly vertically upward from the guide 89 to the pulley 84. A wiper arm 90 having a groove in its face for receiving the filamentary material is located closely above the vessel. The wiper arm 90 removes excess liquid material from the filamentary material so that an even, uniform layer of liquid material remains on the surface of the filamentary material.

When a semiconductor element held between a pair of spindles 16 and 17 moves into the work station 20, the filamentary material 21 contacts the periphery of the semiconductor die 40 which lies between the two end plugs 41 and 42. The semiconductor element rotates in the direction indicated in FIG. 10 and the filamentary material 21 carrying liquid material passes vertically upward. These actions cause liquid material to be transferred from the filamentary material to the region of the periphery of the die of the semiconductor element.

Unloading and Tray Conveying Arrangement Upon subsequent indexes of the conveyor wheel 15 the semiconductor element with the liquid coating applied'is moved into the unloading station 23. At the unloading station the spindles 16 and 17 are located directly underneath the central axis of the conveyor wheel 15. During the dwell period the spindles are at this location, the roller 62 of the spindle lever arm 60 is contacted by the tip 70 of the release lever arm 64 as shown in FIGS. 7 and 9. As explained hereinabove the release cam 68 actuates the lever arm 64 retracting the second spindle 17 and releasing the semiconductor element 10.

The semiconductor element drops into a cavity of a tray 24 which is in position directly beneath the unloading station. The cavities are equally spaced in a line along the length of each tray. The first and last cavities in a tray are spaced from the ends of the tray so that when the ends of two trays abut, the spacing between the last cavity of one tray and the first cavity of the abutting tray is equal to the spacing between adjacent cavities in the same tray. As illustrated in FIG. 12 each of the cavities 95 in a tray 24 has a curvilinear surface configuration such that, regardless of the orientation of a semiconductor element 10 in the cavity, the liquid coated central region cannot come in contact with a surface of the cavity. Thus, the applied coating is not disturbed, and the tray does not pick up any liquid material.

Trays 24 are fed along the track 25 so as to position cavities in sequence under the unloading station by means of an arrangement illustrated in FIGS. 1 and 11. A quantity of empty trays 24 are placed on the supply chute 26 from which they feed downward in order onto the track 25. When a tray 24 moves onto the track 25 from the chute 26, it is engaged by a driving belt which is driven periodically by a stepping motor 101. As the tray 24 moves farther along the track 25 it is engaged by two driving rollers 102 and 103 which are also driven by the motor 101. The motor 101 is coupled to the driving belt 100 and driving rollers 102 and 103 by a chain and gear arrangement 96 which cause the driving belt 100 to move the trays at a slightly faster rate than the driving rollers 102 and 103, thereby insuring that the trays abut. A roller arm 97 holds the trays downward against the track.

The trays are indexed during each index period of the transfer 12 and conveyor wheels 15 by operation of the motor 101 for sufficient time to move the trays 24 along the track 25 a distance equal to the spacing of the cavities 95 in a tray. Operation of the motor 101 is controlled by an arrangement shown in FIGS. 11, 12, and 13. As illustrated in the schematic diagram of FIG. 13, the stepping motor 101 operates under the action of control circuitry 104 when the contact arm of a first switch 105 is in its upper position. When the contact arm 105 is in its lower position as shown in FIG. 13, the control circuitry 104 does not operate the motor. With the contact arm of the first switch 105 down, opening and closing the contact arm of a second switch 106 will cause a supply 107, operating in conjunction with a capacitor 108, to produce pulses at the control circuitry 104 which will operate the stepping motor 101.

As illustrated in FIGS. 11 and 12 the first switch 105 is a microswitch positioned adjacent the track 25 with an actuating arm 109 which is spring biased downward so as to cause the contact arm 105 to be in its lower position when the actuating arm enters a cavity 95. When the arm 109 is out of the cavity 95 the contact arm is in the upper position. The second switch 106 is a magnetic reed switch which is closed by the presence of a magnet. As shown in the detached portion of FIG. 11, several magnets 110 are mounted in a segment ofa disc 111 fixed to the cam shaft 35, and the reed switch 105 is located adjacent the path followed by the magnets 110 as the cam shaft 35 rotates.

The arrangement operates to index the trays along the track the distance of a cavity in the following manner. During a dwell period of the transfer 12 and conveyor wheels 15, the arm 109 of the microswitch 105 and with an end portion adjacent each of the holding members;

means for permitting. the biasing means to urge the second holding member toward the first holding member during a dwell period subsequent to placing of an article between the holding members by the transfer means whereby the article is held between the holding members;

means for rotating a pair of opposed holding members and the article held therebetween .while the holding members are at the work station;

a vessel for containing a supply of liquid material;

a supply of filamentary material;

filamentary material feeding means for guiding filamentary material to pass through liquid material in the vessel and into contact with a point on the central region of an article at the work station, said filamentary material coming in contact with the rotating article while moving in a direction perpendicular to the axis of rotation, whereby liquid material is transferred from the vessel to the central cir cumferential region ofthe article; and

means at the unloading station for overcoming the biasing means and retracting the second holding member along the direction of its linear movement during a dwell period thereby permitting the article to drop from between the opposed holding members.

2. Apparatus in accordance with claim 1 including a plurality of receptacles each adapted to receive'an article;

means for locating a receptacle beneath the unload ing station; and

means for indexing the receptacles in synchronism with the indexing means for indexing the conveyor wheel to position each of the receptacles in sequence beneath the unloading station whereby articles drop from between holding members at the unloading station into receptacles.

3. Apparatus in accordance with claim 1 wherein each article is generally cylindrical and has a length greater than its diameter;

said holding members each have a concave surface facing the concave surface of the opposing holding member of its pair whereby an article is held between the concave surfaces of a pair of opposed holding members; and

said means for rotating a pair of opposed holding members includes means for rotating the pairs of holding members and articles held therebetween while the holding members are being moved to the work station whereby articles tend to become oriented with the direction of their length parallel to the axis of rotation of the holding members.

4. Apparatus in accordance with claim 3 wherein said filamentary material feeding means guides the filamentary material vertically upward from the vessel through the work station, the filamentary material passing between a pair of opposed holding members at the work station in the absence of an article being held by the holding members and into contact with a point on the central circumferential region of an article when an article is located at the work station;

I and including a wiping member adjacent the vessel for contacting the filamentary material moving vertically upward from the vessel and wiping excess liquid from the filamentary material whereby an even, uniform coating of liquid is carried by the filamentary material into contact with the article at the work station. 5. Apparatus in accordance with claim 1 wherein said transfer means includes a vertically disposed transfer wheel having a plurality of article receiving positions equally spaced about its periphery; indexing means for indexing the transfer wheel by rotating the transfer wheel about its central horizontal axis to position the article receiving positions in succession at a pickup station and at said loading station; and article feeding means for presenting articles at the pickup station and placing an article in the article receiving position at the pickup station. 6. Apparatus in accordance with claim 5 wherein each article is generally cylindrical and has a length greater than its diameter; the thickness of said transfer wheel is less than the length of an article; and said article feeding means places an article in an arti cle receiving position with the length of the article disposed horizontally and perpendicular to the plane of the transfer wheel. 7. Apparatus in accordance with claim 6 wherein said article receiving positions are slots in the periphery of the transfer wheel; and said article feeding means includes a horizontally disposed track for permitting the movement of articles therealong in end-to-end relationship, said track being arranged with the end portion perpendicular to the transfer wheel and terminating adjacent a slot in the transfer wheel when the slot is at the pickup station, and means for moving articles along the track whereby an article is moved into a slot when the transfer wheel is indexed to position the slot at the pickup station. 8. Apparatus in accordance with claim 7 including a group of trays, each tray including a plurality of equally spaced receptacles arranged in a line; each receptacle comprising a cavity having curvilinear surfaces of configuration such that the central circumferential region of an article in the cavity is spaced from the surface regardless of the orientation of the article in the cavity; means for locating a tray with a cavity in position beneath the unloading station; and means for indexing a tray in synchronism with the indexing means for indexing the conveyor wheel to position each of the cavities in sequence beneath the unloading station whereby articles drop from between holding members at the unloading station into cavities. 9. Apparatus in accordance with claim 7 wherein said holding members each have a concave surface facing the concave surface of the opposing holding member of its pair whereby an article is held between the concave surfaces of a pair of opposed holding members; and said meansfor rotating a pair of opposed holding members includes means for rotating the pairs of holding members and articles held therebetween while theholding members are being moved to the is in a cavity 95 holding the contact arm 105 in the lower position. The rotational position of the cam shaft 35 is such that the magnets 110 do not affect the reed switch 106 and its contacts are open. During the first portion of an index period, the magnets 110 pass closely adjacent the reed switch 106 causing its contacts to open and close repeatedly. This action produces a series of pulses to the motor control circuitry 104 causing the stepping motor 101 to operate. Movement of the trays 24 along the track 25 forces the arm 109 of the microswitch 105 upwards out of the cavity changing the contact arm to the upper position. With the contact arm of the microswitch 105 in the upper position the control circuitry 104 continues to cause the stepping motor to operate after the magnets 110 have all moved past the reed switch 106. The stepping motor 101 continues to operate moving the trays 24 along the track 25 until the next cavity in sequence causes the arm 109 of the microswitch 105 to be lowered sufficiently to switch the contact arm to the lower position, thereby stopping the motor 101 and resetting the arrangement for starting again during the start of the next index. Thus, during each index the trays 24 are advanced the distance of one cavity 95 placing an empty cavity in position beneath the unloading station to receive a semiconductor element.

As a tray 24 moves along the track 25 beyond the unloading station, it is eventually forced off the track 25 onto the exit chute 27 by a deflector plate 115 and springs 117 and 118. The loaded trays are removed from the chute and then placed in a suitable environment in order to harden the liquid material on the semiconductor elements.

Alternative Embodiment A modified apparatus employing an alternative form of liquid applying mechanism is illustrated by FIG. 14. A rotating disc 120 with flexible bristles 121 along its periphery is substituted for the filamentary material as described hereinabove. Liquid material 122 is contained in a vessel 123, and the level of the liquid in the vessel is maintained constant by a reservoir 124. The lowermost bristles 121 are in the liquid material and bristles at the level of the axis of the disc 120 contact the periphery of the die of the semiconductor element 10 in the rotating spindles 16 and 17 at the work station. The disc 120 is rotated about its horizontal axis in a vertical plane in the direction indicated by an electric motor (not shown). The axis of the disc 120 is at approximately the same level and is parallel to the axis of the spindles at the work station. The bristles 121 of the rotating disc 120 pick up liquid material from the vessel 123 and carry it to the work station where it is transferred to the semiconductor element 10.

Conclusion Apparatus in accordance with the invention has been employed for coating the edges of semiconductor dice of semiconductor elements of the type shown in FIG. 3. The semiconductor elements were 0.094 inch in length and 0.080 inch in diameter and the central region including the die was 0.012 inch thick. The liquid material applied was Dow Corning 646 Junction Coating Resin sold by Dow Corning Corporation, Midland, Mich. This material has a viscosity of 130 centipoises. The filamentary material was 0.010 inch nylon line, and was passed through the liquid and the work station at a rate of about 60 inches per minute. Each semiconductor element remained in position at the work station fora dwell period of two-fifths of a second and was rotated at 50 revolutions per minute. The semiconductor elements were uniformly coated only in the desired region with a proper amount of liquid material. The apparatus processed 6,000 semiconductor elements per hour.

The coated semiconductor elements were dropped into the trays and were treated while remaining in the trays by air drying for one-half hour at room temperature, 2 hours at C, and from 14 to 16 hours at 200C in order to harden the liquid material to form a protective coating at the central circumferential region of the semiconductor element protecting the edges of the junction in the semiconductor die.

While there has been shown and described what are considered preferred embodiments of the present invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention as defined in the appended claims.

What is claimed is:

1. Apparatus for applying liquid material to articles, each article having opposite end portions and a central circumferential region on which the liquid material is to be applied, said apparatus including in combination a conveyor wheel having two opposed vertically disposed plates;

a plurality of first holding members extending horizontally from one plate toward the other plate for a fixed distance, said plurality of first holding member being spaced at equal intervals in a circular pattern around the periphery of the one plate and being individually mounted in the plate for rotation about their horizontal axes;

a like plurality of second holding members extending horizontally from the other plate toward the first holding members to provide a plurality of pairs of opposed holding members, each of said plurality of second holding members being mounted in the plate for rotation about its horizontal axis and for limited linear movement along the direction of its axis;

biasing means for urging each of said second holding members along its direction of linear movement toward the opposed first holding member, the opposed holding members being spaced apart a distance less than the length of an article at the furthest extent of linear movement of the second holding member toward the first holding member;

indexing means for indexing the conveyor wheel by periodically rotating the conveyor wheel about its central horizontal axis through an increment of a circle to position the plurality of pairs of holding members in succession in each of a plurality of locations during a dwell period between indexes, the locations including a loading station, a work station, and an unloading station;

means at the loading station for overcoming the biasing means and retracting the second holding member located at the loading station along the direction of its linear movement to increase the distance between the holding members to greater than the length of an article;

transfer means for placing an article between the two opposed holding members located at the loading station with the direction of its length horizontal work station whereby articles tend to become oriented with the direction of their length parallel to the axis of rotation of the holding members.

10. Apparatus in accordance with claim 9 wherein said filamentary material feeding means guides the filamentary material vertically upward from the vessel through the work station, the filamentary material passing between a pair of opposed holding members at the work station in the absence of an article being held by the holding members and into contact with a point on the central circumferential region of an article when an article is located at the work station;

and including a wiping member adjacent the vessel for contacting the filamentary material moving vertically upward from the vessel and wiping excess liquid from the filamentary material whereby an even, uniform coating of liquid is carried by the filamentary material into contact with the article at the work station.

1 1. Apparatus for applying liquid material to articles,

each article having opposite end portions and a central circumferential region on which the liquid material is to be applied, said apparatus including in combination a conveyor wheel having two opposed vertically disposed plates;

.a plurality of first holding members extending horizontally from one platetoward the other plate for a fixed distance, said plurality of first holding members being spaced at equal intervals in a circular pattern around the periphery of the one plate and being individually mounted in the plate for rotation about their horizontal axes;

a like plurality of second holding members extending horizontally from the other plate toward the first holding members to provide a plurality of pairs of opposed holding members, each of said plurality of second holding members being mounted in the plate for rotation about its horizontal axis and for limited linear movement along the direction of its axis;

biasing means for urging each of said second holding members along its direction of linear movement toward the opposed first holding member, the opposed holding members being spaced apart a distance less than the length of an article at the furthest extent of linear movement of the second holding member toward the first holding member;

indexing means for indexing the conveyor wheel by periodically rotating the conveyor wheel about its central horizontal axis through an increment of a circle to position the plurality of pairs of holding members in succession in each of a plurality of locations during a dwell period between indexes, the locations including a loading station, and an unloading station;

means at the loading station for overcoming the biasing means and retracting the second holding member located at the loading station along the direction of its linear movement to increase the distance between the holding members to greater than the length of an article;

transfer means for placing an article between the two opposed holding members located at the loading station with the direction of its length horizontal and with an end portion adjacent each of the holding mbmbers;

means for permitting the biasing means to urge the secnd holding member toward the first holding member during a dwell period subsequent to placing of an article between the holding members by the transfer means whereby the article is held between the holding members;

means for rotating a pair of opposed holding membersand the article held therebetween while the holding members are at the work station;

a vessel for containing a supply of liquid material;

a vertically disposed circular plate having a plurality of flexible members arranged along the periphery thereof and extending outwardly therefrom generally in the plane of the circular plate;

support means for supporting thecircular plate for rotation about its axis with the flexible members on the lowermost portion of the circular plate in the liquid material in the vessel and with flexible members on another portion of the circular plate in contact with an area of the central region of an article located at the work station, the axis of rotation of the circular plate being parallel to and in the same horizontal plane as the axis of rotation of the opposed holding members at the work station;

means for rotating the circular plate whereby liquid material is transferred from the vessel to the central circumferential region of the rotating article at the work station; and

means at the unloading station for overcoming the biasing means and retracting the second holding member along the direction of its linear movement during a dwell period thereby permitting the article to drop from between the opposed holding members. 12. Apparatus in accordance with claim 10 including a plurality of receptacles each adapted to receive an article; means for locating a receptacle beneath the unloading station; and means for indexing the receptacles in synchronism with the indexing means for indexing the conveyor wheel to position each of the receptacles in sequence beneath the unloading station whereby articles drop from between holding members at the unloading station into receptacles. 13. Apparatus in accordance with claim 11 wherein each article is generally cylindrical and has a length greater than its diameter; said holding members each have a concave surface facing the concave surface of the opposing holding member of its pair whereby an article is held between the concave surfaces of a pair of opposed holding members; and said means for rotating a pair of opposed holding members includes means for rotating the pairs of holding members and articles held therebetween while the holding members are being moved to the work station whereby articles tend to become oriented with the direction of their length parallel to the axis of rotation of the holding members. 14. Apparatus in accordance with claim 11 wherein said transfer means includes a vertically disposed transfer wheel having a plurality of article receiving positions equally spaced about its periphery;

indexing means for indexing the transfer wheel by rotating the transfer wheel about its central horizontal axis to position the article receiving positions in succession at a pickup station and at said loading station; and article feeding means for presenting articles at the pickup station and placing an article in the article receiving position at the pickup station. 15. Apparatus in accordance with claim 14 wherein each article is generally cylindrical and has a length greater than its diameter; the thickness of said transfer wheel is less than the length of an article; and said article feeding means places an article in an article receiving position with the length of the article disposed horizontally and perpendicular to the plane of the transfer wheel. 16. Apparatus in accordance with claim 15 wherein said article receiving positions are slots in the periphery of the transfer wheel; and said article feeding means includes a horizontally disposed track for permitting the movement of articles therealong in end-to-end relationship, said track being arranged with the end portion perpendicular to the transfer wheel and terminating adjacent a slot in the transfer wheel when the slot is at the pickup station, and means for moving articles along the track whereby an article is moved into a slot when the transfer wheel is indexed to position the slot at the pickup station.

17. Apparatus in accordance with claim 16 including a group of trays, each tray including a plurality of equally spaced receptacles arranged in a line;

each receptacle comprising a cavity having curvilinear surfaces of configuration such that the central circumferential of an article in the cavity is spaced from the surface regardless of the orientation of the article in the cavity;

means'for locating a tray with a cavity in position beneath the unloading station; and

means for indexing a tray in synchronism with the indexing means for indexing the conveyor wheel to position each of the cavities in sequence beneath the unloading station whereby articles drop from between holding members at the unloading station into cavities.

18. Apparatus in accordance with claim 16 wherein said holding members each have a concave surface facing the concave surface of the opposing holding member of its pair whereby an article is held between the concave surfaces of a pair of opposed holding members; and

said means for rotating a pair of opposed holding members includes means for rotating the pairs of holding members and articles held therebetween while the holding members are being moved to the work station whereby articles tend to become oriented with the direction of their length parallel to the axis of rotation of the holding members. 

1. Apparatus for applying liquid material to articles, each article having opposite end portions and a central circumferential region on which the liquid material is to be applied, said apparatus including in combination a conveyor wheel having two opposed vertically disposed plates; a plurality of first holding members extending horizontally from one plate toward the other plate for a fixed distance, said plurality of first holding member being spaced at equal intervals in a circular pattern around the periphery of the one plate and being individually mounted in the plate for rotation about their horizontal axes; a like plurality of second holding members extending horizontally from the other plate toward the first holding members to provide a plurality of pairs of opposed holding members, each of said plurality of second holding members being mounted in the plate for rotation about its horizontal axis and for limited linear movement along the direction of its axis; biasing means for urging each of said second holding members along its direction of linear movement toward the opposed first holding member, the opposed holding members being spaced apart a distance less than the length of an article at the furthest extent of linear movement of the second holding member toward the first holding member; indexing means for indexing the conveyor wheel by periodically rotating the conveyor wheel about its central horizontal axis through an increment of a circle to position the plurality of pairs of holding members in succession in each of a plurality of locations during a dwell period between indexes, the locations including a loading station, a work station, and an unloading station; means at the loading station for overcoming the biasing means and retracting the second holding member located at the loading station along the direction of its linear movement to increase the distance between the holding members to greater than the length of an article; transfer means for placing an articlE between the two opposed holding members located at the loading station with the direction of its length horizontal and with an end portion adjacent each of the holding members; means for permitting the biasing means to urge the second holding member toward the first holding member during a dwell period subsequent to placing of an article between the holding members by the transfer means whereby the article is held between the holding members; means for rotating a pair of opposed holding members and the article held therebetween while the holding members are at the work station; a vessel for containing a supply of liquid material; a supply of filamentary material; filamentary material feeding means for guiding filamentary material to pass through liquid material in the vessel and into contact with a point on the central region of an article at the work station, said filamentary material coming in contact with the rotating article while moving in a direction perpendicular to the axis of rotation, whereby liquid material is transferred from the vessel to the central circumferential region of the article; and means at the unloading station for overcoming the biasing means and retracting the second holding member along the direction of its linear movement during a dwell period thereby permitting the article to drop from between the opposed holding members.
 2. Apparatus in accordance with claim 1 including a plurality of receptacles each adapted to receive an article; means for locating a receptacle beneath the unloading station; and means for indexing the receptacles in synchronism with the indexing means for indexing the conveyor wheel to position each of the receptacles in sequence beneath the unloading station whereby articles drop from between holding members at the unloading station into receptacles.
 3. Apparatus in accordance with claim 1 wherein each article is generally cylindrical and has a length greater than its diameter; said holding members each have a concave surface facing the concave surface of the opposing holding member of its pair whereby an article is held between the concave surfaces of a pair of opposed holding members; and said means for rotating a pair of opposed holding members includes means for rotating the pairs of holding members and articles held therebetween while the holding members are being moved to the work station whereby articles tend to become oriented with the direction of their length parallel to the axis of rotation of the holding members.
 4. Apparatus in accordance with claim 3 wherein said filamentary material feeding means guides the filamentary material vertically upward from the vessel through the work station, the filamentary material passing between a pair of opposed holding members at the work station in the absence of an article being held by the holding members and into contact with a point on the central circumferential region of an article when an article is located at the work station; and including a wiping member adjacent the vessel for contacting the filamentary material moving vertically upward from the vessel and wiping excess liquid from the filamentary material whereby an even, uniform coating of liquid is carried by the filamentary material into contact with the article at the work station.
 5. Apparatus in accordance with claim 1 wherein said transfer means includes a vertically disposed transfer wheel having a plurality of article receiving positions equally spaced about its periphery; indexing means for indexing the transfer wheel by rotating the transfer wheel about its central horizontal axis to position the article receiving positions in succession at a pickup station and at said loading station; and article feeding means for presenting articles at the pickup station and placing an article in the article receiving position at the pickup station.
 6. Apparatus in accordance with claim 5 wherein each article is generally cylindrical and has a length greater than its diameter; the thickness of said transfer wheel is less than the length of an article; and said article feeding means places an article in an article receiving position with the length of the article disposed horizontally and perpendicular to the plane of the transfer wheel.
 7. Apparatus in accordance with claim 6 wherein said article receiving positions are slots in the periphery of the transfer wheel; and said article feeding means includes a horizontally disposed track for permitting the movement of articles therealong in end-to-end relationship, said track being arranged with the end portion perpendicular to the transfer wheel and terminating adjacent a slot in the transfer wheel when the slot is at the pickup station, and means for moving articles along the track whereby an article is moved into a slot when the transfer wheel is indexed to position the slot at the pickup station.
 8. Apparatus in accordance with claim 7 including a group of trays, each tray including a plurality of equally spaced receptacles arranged in a line; each receptacle comprising a cavity having curvilinear surfaces of configuration such that the central circumferential region of an article in the cavity is spaced from the surface regardless of the orientation of the article in the cavity; means for locating a tray with a cavity in position beneath the unloading station; and means for indexing a tray in synchronism with the indexing means for indexing the conveyor wheel to position each of the cavities in sequence beneath the unloading station whereby articles drop from between holding members at the unloading station into cavities.
 9. Apparatus in accordance with claim 7 wherein said holding members each have a concave surface facing the concave surface of the opposing holding member of its pair whereby an article is held between the concave surfaces of a pair of opposed holding members; and said means for rotating a pair of opposed holding members includes means for rotating the pairs of holding members and articles held therebetween while the holding members are being moved to the work station whereby articles tend to become oriented with the direction of their length parallel to the axis of rotation of the holding members.
 10. Apparatus in accordance with claim 9 wherein said filamentary material feeding means guides the filamentary material vertically upward from the vessel through the work station, the filamentary material passing between a pair of opposed holding members at the work station in the absence of an article being held by the holding members and into contact with a point on the central circumferential region of an article when an article is located at the work station; and including a wiping member adjacent the vessel for contacting the filamentary material moving vertically upward from the vessel and wiping excess liquid from the filamentary material whereby an even, uniform coating of liquid is carried by the filamentary material into contact with the article at the work station.
 11. Apparatus for applying liquid material to articles, each article having opposite end portions and a central circumferential region on which the liquid material is to be applied, said apparatus including in combination a conveyor wheel having two opposed vertically disposed plates; a plurality of first holding members extending horizontally from one plate toward the other plate for a fixed distance, said plurality of first holding members being spaced at equal intervals in a circular pattern around the periphery of the one plate and being individually mounted in the plate for rotation about their horizontal axes; A like plurality of second holding members extending horizontally from the other plate toward the first holding members to provide a plurality of pairs of opposed holding members, each of said plurality of second holding members being mounted in the plate for rotation about its horizontal axis and for limited linear movement along the direction of its axis; biasing means for urging each of said second holding members along its direction of linear movement toward the opposed first holding member, the opposed holding members being spaced apart a distance less than the length of an article at the furthest extent of linear movement of the second holding member toward the first holding member; indexing means for indexing the conveyor wheel by periodically rotating the conveyor wheel about its central horizontal axis through an increment of a circle to position the plurality of pairs of holding members in succession in each of a plurality of locations during a dwell period between indexes, the locations including a loading station, and an unloading station; means at the loading station for overcoming the biasing means and retracting the second holding member located at the loading station along the direction of its linear movement to increase the distance between the holding members to greater than the length of an article; transfer means for placing an article between the two opposed holding members located at the loading station with the direction of its length horizontal and with an end portion adjacent each of the holding members; means for permitting the biasing means to urge the second holding member toward the first holding member during a dwell period subsequent to placing of an article between the holding members by the transfer means whereby the article is held between the holding members; means for rotating a pair of opposed holding members and the article held therebetween while the holding members are at the work station; a vessel for containing a supply of liquid material; a vertically disposed circular plate having a plurality of flexible members arranged along the periphery thereof and extending outwardly therefrom generally in the plane of the circular plate; support means for supporting the circular plate for rotation about its axis with the flexible members on the lowermost portion of the circular plate in the liquid material in the vessel and with flexible members on another portion of the circular plate in contact with an area of the central region of an article located at the work station, the axis of rotation of the circular plate being parallel to and in the same horizontal plane as the axis of rotation of the opposed holding members at the work station; means for rotating the circular plate whereby liquid material is transferred from the vessel to the central circumferential region of the rotating article at the work station; and means at the unloading station for overcoming the biasing means and retracting the second holding member along the direction of its linear movement during a dwell period thereby permitting the article to drop from between the opposed holding members.
 12. Apparatus in accordance with claim 10 including a plurality of receptacles each adapted to receive an article; means for locating a receptacle beneath the unloading station; and means for indexing the receptacles in synchronism with the indexing means for indexing the conveyor wheel to position each of the receptacles in sequence beneath the unloading station whereby articles drop from between holding members at the unloading station into receptacles.
 13. Apparatus in accordance with claim 11 wherein each article is generally cylindrical and has a length greater than its diameter; said holding members each have a concave surface facing the concave surface of the opposing holding member of its pair whereby an artIcle is held between the concave surfaces of a pair of opposed holding members; and said means for rotating a pair of opposed holding members includes means for rotating the pairs of holding members and articles held therebetween while the holding members are being moved to the work station whereby articles tend to become oriented with the direction of their length parallel to the axis of rotation of the holding members.
 14. Apparatus in accordance with claim 11 wherein said transfer means includes a vertically disposed transfer wheel having a plurality of article receiving positions equally spaced about its periphery; indexing means for indexing the transfer wheel by rotating the transfer wheel about its central horizontal axis to position the article receiving positions in succession at a pickup station and at said loading station; and article feeding means for presenting articles at the pickup station and placing an article in the article receiving position at the pickup station.
 15. Apparatus in accordance with claim 14 wherein each article is generally cylindrical and has a length greater than its diameter; the thickness of said transfer wheel is less than the length of an article; and said article feeding means places an article in an article receiving position with the length of the article disposed horizontally and perpendicular to the plane of the transfer wheel.
 16. Apparatus in accordance with claim 15 wherein said article receiving positions are slots in the periphery of the transfer wheel; and said article feeding means includes a horizontally disposed track for permitting the movement of articles therealong in end-to-end relationship, said track being arranged with the end portion perpendicular to the transfer wheel and terminating adjacent a slot in the transfer wheel when the slot is at the pickup station, and means for moving articles along the track whereby an article is moved into a slot when the transfer wheel is indexed to position the slot at the pickup station.
 17. Apparatus in accordance with claim 16 including a group of trays, each tray including a plurality of equally spaced receptacles arranged in a line; each receptacle comprising a cavity having curvilinear surfaces of configuration such that the central circumferential of an article in the cavity is spaced from the surface regardless of the orientation of the article in the cavity; means for locating a tray with a cavity in position beneath the unloading station; and means for indexing a tray in synchronism with the indexing means for indexing the conveyor wheel to position each of the cavities in sequence beneath the unloading station whereby articles drop from between holding members at the unloading station into cavities.
 18. Apparatus in accordance with claim 16 wherein said holding members each have a concave surface facing the concave surface of the opposing holding member of its pair whereby an article is held between the concave surfaces of a pair of opposed holding members; and said means for rotating a pair of opposed holding members includes means for rotating the pairs of holding members and articles held therebetween while the holding members are being moved to the work station whereby articles tend to become oriented with the direction of their length parallel to the axis of rotation of the holding members. 